Plastic films containing either natural or synthetic zeolites were disclosed to provide packaging materials for fresh produce. It was reported in several patents of invention that the films can keep the freshness of fresh produce packaged. Examples of the inventions are U.S. Pat. Nos. 4,814,364, 4,840,823 and 4,847,145. Furthermore, EP 1170327 A1 discloses the plastic articles, e.g., plastic films, containing organophillic zeolites dispersed in polymer matrix. Said plastic films can selectively adsorb volatile organic compounds, in particular ethylene. Nevertheless, the aforementioned inventions have disadvantages since adsorption capability of said films is limited by an amount of zeolite incorporated. Therefore, there is a disclosure of another prior invention in the publication of Thailand Patent Application No. 98017 (27 Aug. 2009) to overcome the mentioned disadvantage. The invention discloses packaging film containing 5%-30% by weight of fine zeolite particles selected from the group consisting of zeolite beta, ZSM-5 and silicalite. Said zeolite is dispersed in polymer blend in which one component is polymer having ethylene transmission rate higher than 36,000 cubic centimeters/square meters.day. Said film is obtained by conventional thermoplastic processing. Additionally, said film has ethylene transmission rate in the range of 36,000-90,000 cubic centimeters/square meters.day and can retard ripening process and extend shelf life of fruits and vegetable. However, ethylene selectivity of such films is not high enough for packing ethylene-sensitive produces. Accordingly, it is an objective of the present invention to disclose formula of masterbatch for preparing plastic films with high ethylene permselectivity, i.e., high in both permeability and selectivity, and the plastic films produced therefrom. The films from this invention have high ethylene permselectivity and are thus suitable for ethylene-sensitive commodities.
There have been several recent research studies on the development of gas separation membranes containing molecular sieve/zeolite particles uniformly dispersed in polymer matrix. It was reported that minute cracks and voids were presented at the interface of molecular sieve/zeolite particles and polymer matrix and, consequently, lessen the separation capability, in particular gas selectivity. Surface modification of zeolite particles can be carried out to improve particle dispersion and interfacial adhesion. Gas permeability and selectivity of the membranes containing such modified zeolite were, thus, enhanced. The inventions are; for example, U.S. Pat. No. 6508860 B1 discloses the gas separation membrane containing zeolites, e.g., chabazite-type zeolites, modified by monofunctional organosilane compound that can react with silanol groups on the zeolite surface. With only one reacting group per molecule, said organosilane molecules will not block the pores and channels in the zeolite structure. Said organosilane compounds were 3-aminopropyldimethyl ethoxysilane (APDMS), 3-isocyanatopropyldimethylchlorosilane (ICDMS) and 3-aminopropyldiisopropyl ethoxysilane (APDIPS). In addition, this invention points out the benefit of surface modification of zeolite that can provide good particle dispersion, leading to improve gas selectivities, especially oxygen and carbon dioxide. However, disclosed fabrication method of said membrane is the conventional method, i.e., solution casting. Said method, however, is well known to those skilled in the art that is troublesome and time-consuming.
U.S. Pat. No. 5891376 and Publication of Patent Application AU-B-83930/91 discloses an invention of controlled permeability film and process for producing said film wherein the film includes polyolefins and inert porous fillers including natural zeolite and natural zeolite of which surface is modified by silane coupling agent. Said film has reduced ratio of CO2 permeability to O2 permeability. Said silane coupling agents are selected from methyl-trichloro-silane and trichloro-octadecyl-silane to provide the reduced ratio of CO2 permeability to O2 permeability. Evidently, said coupling agents does not facilitate ethylene transports to enhance ethylene permeability which is an objective of this present invention.
This disclosed invention aims to develop plastic film having zeolite of which surface was modified by chemicals with specific functional groups to provide good particle dispersion, good particle-polymer interfacial adhesion and, thus, improved ethylene permselectivity. Accordingly, the invention discloses masterbatch for preparing the plastic films with high ethylene permselectivity and the plastic films produced therefrom.